The epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are crucial for the regulation of cellular plasticity during liver fibrosis. Transforming growth factor (TGF)-β1 is an important cytokine for the induction of the EMT in liver fibrosis. TGF-β1 signaling induces the EMT through various signaling mechanisms and is the predominant agent mediating these fibrotic changes. Chronic exposure to TGF-β1 induces the transition of hepatocytes to collagen-producing mesenchymal cells, prolonged exposure of hepatocytes to TGF-β1 increases the expression of collagen and induces cytoskeletal rearrangement that resembles the EMT. These morphological and molecular alterations may provide the foundation for liver fibrosis. This review discussed the relation and mechanisms between EMT and liver fibrosis and ulteriorly elaborated on TGF-β1 induced EMT and each of their roles in liver fibrosis. Better understanding of the cellular and molecular characteristics of the cirrhotic hepatocyte may enable the development of chemo-preventative agents for liver fibrosis.

ABSTRACT. This study was designed to show whether rat liver epithelial cells could undergo epithelial-mesenchymal transition (EMT), thereby directly contributing to liver fibrosis. The role of the ratio of transforming growth factor-β1 (TGF-β1)/bone morphogenetic protein-7 (BMP-7) was evaluated in the progression of EMT or mesenchymal-epithelial transition. Primary rat liver epithelial cells were stimulated with different ratios of TGF-β1/BMP-7 and examined for evidence of transition to a mesenchymal or epithelial phenotype. Liver sections were labeled to detect antigens associated with liver epithelial cells [E-cadherin (E-cad)], EMT [fibroblast-specific protein-1 (FSP-1), vimentin], myofibroblasts [α-smooth muscle actin (α-SMA)], and intracellular signal-transduction mediated by forming liver fibrosis undergo EMT, resulting in the formation of invasive fibroblasts; this process may be driven or impeded by a response to local TGF-β1 or BMP-7. BMP-7 downregulated α-SMA and phosphorylated Smad2/3. Stimulation of cultured cells with TGF-β1 induced the expression of pSmad2/3, FSP-1, and α-SMA. Stimulation of cultured cells with BMP-7 induced the expression of E-cad. We demonstrated that the cells upregulated E-cad release compared with untreated cells, but TGF-β1 was different. We found that the equilibrium of the ratio of TGF-β1/BMP-7 was 1/10. In summary, the mechanism for this process was not determined. Demonstration of the contribution of what the ratio of TGF-β1/BMP-7 induced to EMT to the chronic liver diseases would provide a new basis for understanding pathogenesis and potential treatment.

ABSTRACT. Serum liver enzyme levels are often used effectively for the evaluation of nonalcoholic fatty liver disease (NAFLD). We aimed to investigate the associations between serum liver enzyme levels and risks for NAFLD in over 8000 cases in a large-scale analysis. A cross-sectional survey with multiple stages and random samplings was performed from May 2007 to May 2009 on 8102 workers at Tongji University. A questionnaire was given, assessments of physical measurements, plasma glucose, lipid profiles, and liver enzymes were made, and real-time liver ultrasounds conducted. The prevalence of NAFLD in Tongji University was 22.2%. It was higher in males than in females (P = 0.0023). The body mass index, waist-to-hip ratio, serum total triglycerides, serum total cholesterol, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutamyl transferase (GGT) values were all higher in the NAFLD group than in the control group. For moderate and severe NAFLD patients, the ALT, AST and GGT values were significantly Factors influencing nonalcoholic fatty liver disease increased, high density lipoprotein cholesterol was decreased, and drinking much, heavy entertainment and less exercise were more prevalent (P < 0.001). There were strong correlations between serum liver enzyme levels and NAFLD (P < 0.001), with GGT being a more sensitive marker for NAFLD than ALT or AST. ALT and GGT were independent predictors for NAFLD, and GGT was a better predictor than ALT for NAFLD.

The aim of this study was to explore the molecular mechanism of the bone morphogenetic protein-7 (BMP-7) downregulation of Snail-mediated E-cadherin repression and mesenchymal-epithelial transition (MET) induction, since little is presently known about this issue. In this study, our aim was to elucidate the underlying mechanism by which cells acquire liver fibrosis characteristics after epithelial-mesenchymal transition (EMT). Cell cultures were exposed to Snail alone or in the presence of BMP-7; control cultures were exposed to medium only. The expression of the mRNA encoding α-smooth muscle actin (α-SMA), Snail and E-cadherin in rat liver epithelial cells was determined by real-time quantitative PCR (RT-PCR) and the main results were confirmed by ELISA. Cell differentiation was determined by analysis of the expression of α-SMA, Snail and E-cadherin by western blotting and co-immunoprecipitation. We demonstrated Snail-induced upregulation of mRNAs encoding α-SMA and downregulation of mRNAs encoding E-cadherin in rat liver epithelial cells when compared with unstimulated cells, and confirmed these results at the protein level. BMP-7 downregulated Snail-induced α-SMA and upregulated E-cadherin release compared with untreated and Snail-treated cells. In summary, we demonstrated that BMP-7 induces MET through decreased downregulation of Snail. In addition, Snail1 directly regulates Nanog promoter activity. Notch signaling is also involved in this process.